As communications networks, such as the Internet, carry more and more traffic, efficient use of the bandwidth available in the network becomes more and more important. Switching technology was developed in order to reduce congestion and associated competition for the available bandwidth. Switching technology works by restricting traffic. Instead of broadcasting a given data packet to all parts of the network, switches are used to control data flow such that the data packet is sent only along those network segments necessary to deliver it to the target node. The smaller volume of traffic on any given segment results in few packet collisions on that segment and, thus, the smoother and faster delivery of data. A choice between alternative paths is usually possible and is typically made based upon current traffic patterns.
The intelligent routing of data packets with resultant reduction in network congestion can only be effected if the network topology is known. The topology of a network is a description of the network which includes the location of and interconnections between nodes on the network. The word “topology” refers to either the physical or logical layout of the network, including devices, and their connections in relationship to one another. Information necessary to create the topology layout can be derived from tables stored in network devices such as hubs, bridges, and switches. The information in these tables is in a constant state of flux as new entries are being added and old entries time out. Many times there simply is not enough information to determine where to place a particular device.
Switches examine each data packet that they receive, read the source addresses, and log those addresses into tables along with the switch ports on which the packets were received. If a packet is received with a target address without an entry in the switches table, the switch receiving it broadcasts that packet to each of its ports. When the switch receives a reply, it will have identified where the new node lies.
In a large network with multiple possible paths from the switch to the target node, this table can become quite large and may require a significant amount of the switch's resources to develop and maintain. As an additional complication, the physical layout of devices and their connections are typically in a state of constant change. Devices are continually being removed from, added to, and moved to new physical locations on the network. To be effectively managed, the topology of a network must be accurately and efficiently ascertained, as well as maintained.
Existing mapping methods have limitations that prevent them from accurately mapping topological relationships. Multiple connectivity problems are one sort of difficulty encountered by existing methods. For example, connectors such as routers, switches, and bridges may be interconnected devices in a network. Some existing methods assume that these devices have only a single connection between them. In newer devices, however, it is common for manufacturers to provide multiple connections between devices to improve network efficiency and to increase capacity of links between the devices. The multiple connectivity allows the devices to maintain connection, in case one connection fails. Methods that do not consider multiple connectivity do not present a complete and accurate topological map of the network.
Another limitation of existing topology methods is the use of a single reference to identify a device. Existing methods use a reference interface or a reference address in a set of devices to orient all other devices in the same area. These methods assumed that every working device would be able to identify, or “hear,” this reference and identify it with a particular port of the device. With newer devices, however, it is possible that the same address or reference may be heard out of multiple ports of the same device. It is also possible that the address or reference may not be heard from any ports, for example, if switching technology is used.
Still another limitation of existing mapping systems is that they require a complete copy of the topological database to be stored in memory. In larger networks, the database is so large that this really is not feasible, because it requires the computer to be very large and expensive.
Still another difficulty with existing systems is that they focus on the minutia without considering the larger mapping considerations. Whenever an individual change in the system is detected, existing methods immediately act on that change, rather than taking a broader view of the change in the context of other system changes. For example, a device may be removed from the network temporarily and replaced with its ports reversed. In existing systems, this swapped port scenario could require hundreds or thousands of changes because the reference addresses will have changed for all interconnected devices.
Still another disadvantage of existing methods is that they use a continuous polling paradigm. These methods continuously poll network addresses throughout the day and make decisions based on those continuous polling results. This creates traffic on the network that slows other processes.
Still another limitation of existing methods is the assumption that network parts of a particular layer would be physically separated from other parts. Network layer 1 may represent the physical cabling of the network, layer 2 may represent the device connectivity, and layer 3 may represent a higher level of abstraction, such as the groupings of devices into regions. Existing methods assume that all layer 3 region groupings are self-contained, running on the same unique physical networking. However, in an internet protocol (IP) network, multiple IP domains may co-exist on the same lower layer networking infrastructure. It has become common for a network to employ a virtual local area network (LAN) to improve security or to simplify network maintenance, for example. Using virtual LANs, a system may have any number of different IP domains sharing the same physical connectivity. As a result, existing methods create confusion with respect to topological mapping because networks with multiple IP addresses in different subnets for the infrastructure devices cannot be properly represented because they assume the physical separation of connectivity for separate IP domains. Still another limitation of existing methods is that they do not allow topological loops, such as port aggregation or trunking, and switch meshing.